1. Field of the Invention
The present invention relates to molecular magnetic protein, in particular to a highly magnetically aligned metallothionin containing manganese and cadmium.
2. Description of the Related Art
Molecular magnets, for which we refer to organic or biological molecules bearing magnetic moments, offer new opportunity in the creation of novel, low dimensional, nano-structured materials. There have been emphases on those molecular magnets that operate at room temperatures or above (Petty, M C; Bryce, M R; Bloor, D. Introduction to Molecular Electronics; Edward Arnold: London, 1995).
Metallothionein (MT) plays a role of detoxication and serves as an antioxidant in mammalian. It spreads widely in many organs, but most frequently in the livers and the kidneys. MT is a thermally stable protein and contains 61 amino acid units. It has 20 conserved cysteines (Cys) with no disulfide bond detected (Eaton et al., Toxicology and Applied Pharmacology (1985) 78, 158–162,). In addition, its secondary structure contains no α-helix or β-sheet. These Cys' form two metal binding clusters located at the carboxyl (α-domain) and amino (β-domain) terminals of MT.
As evidenced from X-ray crystallography and solution NMR studies, the purified native metallothionein-2 (MT-2) from rabbit, contained seven metal ions (i.e., Zn2+/Cd2+) distributed in two metal clusters (see e.g., Robbins et al., J. Mol. Biol. (1991) 221, 1269–1293; Messerle et al., J. Mol. Biol. (1992) 225, 433–443). Four of the seven ions compose an (M4S11)3− cluster in the α-domain, and the rest three compose an (M3S9)3− cluster in the β-domain, where M denotes metal ions (Zn2+, Cd2+, or others). (See e.g., Otvos et al., Proc. Natl. Acad. Sct. USA 77, 7094–7098 (1980); Boulange et al., Proc. Natl. Acad. Sci. USA, (1983) 80, 1501–1505; Chang et al., Protein Engineering (1996) 9, 1165–1172). These two ion-binding clusters located approximately three to four nanometers within each other (see Robbins et al., J. Mol. Biol. (1991) 221, 1269–1293) and have similar characteristics as the “semiconductor MS” compounds (see e.g., Wei et al., Physical Review Letters, (1986) 56, 2391–2394; Spaldin et al., Magnetic Materials. Fundamentals and Device Applications (2003)).
The inventors have now developed molecular magnets produced from metallothionein. To the inventors' knowledge, this is the first report on molecular magnet concerning biological systems that is functional at an operating temperature as high as 300 K.